Egg size

I have a broody bournville who is on day 2 of sitting on her eggs. I was just wondering if the size of the eggs affect their growth ect.
4 out of 12 of them (eggs) are fairly small and this is the first time I've had a broody hen with cockerals. So just any information would be great
I dont really know how or where to tag things so I hope I've done this right